The 261 should bolt in on the same mounts as the original engine. On later models, the plate between the timing cover and the block might have to be drilled for the "bird leg" front mounts, but the earlier engines with the flat rubber mount in the center of that plate are a direct bolt-in, I believe. You might have to drill a couple of holes to bolt the flat mount to the timing plate if the 59 engine has the side mounts instead of the one at the front.
Jerry
